Solvent extraction of unsaturated hydrocarbons



Sept. 26, 1950 R. M. COLE 2,523,681

SOLVENT EXTRACTION 0F UNSATURATED HYDROCARBONS Filed Sept. 22, 1947 Un sai'umfed Hydrocarbon rsi'r'lppcr Exi'rador 19 Hydrocarbon Reqznc rafor h s MWQLWW Patented Sept. 26, 1950 2,523,681

SOLVENT Ex'r'aAo'rroN or unsa'runa'mn mmnocaanous Robert M. Cole, Oakland, Caliit, assignor to Shell Development Company, San Francisco, Call, a corporation of Delaware Application September 22, 1941, Serial No. 775,456

11 Claims. (Cl. Mill-.877)

. 1 This invention relates to the separation and concentration of unsaturated from less unsaturated hydrocarbons, and is particularly applicable to the separation and concentration of limited by any theory relative thereto. By absorption, extraction, and terms of similar im'- port, as used herein, is meant the taking up or the unsaturated hydrocarbon by the solution irrespective of the exact mechanism thereof.

The present invention provides a process for the separation and concentration of unsaturated hydrocarbons from fluid mixtures containing them, which process comprises contacting said olefins from fluid hydrocarbon mixtures. 5 fluid mixtures containing unsaturated hydrocar- Processes for separating oleflns from hydrocarbons with a solution of a silver salt in water and hen mixtures by contacting the mixtures with a phenol, thereby absorbing or dissolving the unsolutions of heavy metal salts capable of forming saturated hydrocarbon in said solution, and reversible complexes with said olefins, whereby separating the resulting solution containing the said oleflns are extracted by said solution, have unsaturated hydrocarbon from the remaining been described. The presence of a neutral waterunabsorbed components of said mixture. The soluble organic compound, such as ethylene glypresent invention may be employed in connection col, has been stated to increaseolefin absorption. with the separation and concentration of many However, the presence of the heretofore described different unsaturated hydrocarbons from a solutizers, as has been found, does not increase 5 variety of fluid mixtures containing them. The absorption, while maintaining high selectivity, to term fluid, as used herein, is-meant to include the extent desired for commercial operations. both gases and liquids. For example, in one em- It is therefore an object of the present invenbodiment, the invention may be employed for the tion to provide an improved process for the sepaseparation of olefins such as ethylene, propylene ration of unsaturatedhydrocarbons from fluid and butylene from gaseous hydrocarbon mixhydrocarbon mixtures containing them. A furtures, or such gaseoim mixtures may be liquefied ther object is to separate unsaturated hydrocaras by compression and the olefins separated from bons from less unsaturated hydrocarbons. Anthe liquefied mixture. Another embodiment of other object is to provide an improved process the present invention contemplates the separafor separating oleiins from olefinic cracked hytion of normally liquid unsaturated hydrocardrocarbon mixtures. A still further object is to bons, such as pentenes, hexenes, heptenes, cycloseparate olefins, in substantially pure form, from pentenes, cyclohexenes, and the like, from liquid other hydrocarbons. Still another object is to mixtures containing them. The invention may rovide for the storage and transportation of also be used to separate aromatic compounds normally gaseous unsaturated hydrocarbons. containing an unsaturated aliphatic side chain Further objects and advantages of the present from the corresponding saturated compound, the invention will be readily apparent from the folaromatic ring being considered to be saturated lowing description. v in the sense of the term as used herein and in It has now been found that the addition 01' the appended claims; or from other saturated phenol to an aqueous solution of a water soluble compounds, such as the separation of styrene silver salt, such as silver nitrate, greatly increases from ethyl benzene. Unsaturated hydrocarbons the absorption of oleflns therein, while the high may also be separated from nonhydrocarbons, selectivit of the absorbing solution for olefins such as thiophene, furan, pyrrole, ethers, thioover saturated hydrocarbons remains substan ethers, their derivatives, and the like, in accordtiallyunaffected. The present invention, there- 40 ance with the present invention A further fore, provides an improved method of increasing application of the present invention is the sepathe solubility of hydrocarbons in aqueous silver ration and concentration of unsaturated from salt solutions without loss of olefinic selectivity, less unsaturated hydrocarbons, such as the sepaas fully described hereinafter. There may be ration of cyclopentadiene from cyclopentene, or some doubt as to whether the absorption of un- 5 the Sep ra of u iene ro bu y e e, and saturated hydrocarbons, as herein described, is the separation of acetylenic hydrocarbons from physical or due to the formation of a complex mixtures containing them. material between the unsaturated hydrocarbon The present invention is especially applicable and one or more components of the solution, and to the separation of oleflns from hydrocarbons it is'not desired that the present invention be 5 of the gasoline range obtained by thermal or catalytic cracking of various petroleum oils, such as crudes, residues, distillates or gases. While olefmic .mixtures of hydrocarbons of various molecular weights may be treated in accordance with the present invention, mixtures of hydrocarbons having relatively small numbers of carbon atoms to the molecule, i. e., relatively low molecular weight hydrocarbons, such as for example hydrocarbons of from 2 to 8 carbon atoms, are especially suitable for employment therein. Thus, for example, the process of the present invention may be used to treat mixtures of hydrocarbons having from 2 to 8 carbon atoms and containing the desired olefins, which mixtures may be obtained, for example, by the vapor phase cracking of petroleum oils.

In accordance with the present invention, a hydrocarbon fluid containing one or more unsaturated hydrocarbons, such as olefins, is contacted with a solution containing a water soluble silver salt, water and phenol. It has been found that such solutions absorb surprisingly large amounts of olefins. For example, phenol-solutized aqueous silver nitrate solutions absorb from about to or more, of their own volume of 5 carbon atom olefins, whereas the same solutions solutized with ethylene glycol, for example, absorb only about 4% of their volume, while unsolutized aqueous solutions absorb only about 1 to 2% of their volume. Other olefins ma be absorbed to an even greater extent, with the superiority of the phenol solutized solution remaining markedly predominant.

In carrying out the process of the present invention considerable latitude is permissible in the composition of the absorbing solution. Best results will be obtained, however, if the limits described below are observed. When silver nitrate, a preferred water soluble salt of the present invention is employed, it is preferred to have the silver nitrate and phenol present in such quantities that the weight ratio of silver nitrate to phenol is from about 0.4 to about 3, and in most instances excellent results are achieved when said ratio is from about 1 to about 2. At the same time the water concentration may advantageously be from about 3 to about by weight of the absorbing solution, and preferably from about 10% to about 22% by weight. The quantity of water present may be varied, but is preferably kept as small as is consistent with the solubility of silver nitrate in the mixture. For example, with a weight ratio of silver nitrate to phenol of l the quantity of water present may advantageously be about 10 to 12% by weight of the absorbing solution. As the silver nitrate to phenol ratio is decreased, the water concentration may be decreased, e. g., at a ratio of 0.5, the water concentration may advantageously be about 5% by weight and high absorption of olefins obtained. Even though the selectivity for olefins may decrease at relatively low water concentrations, in many instances the decrease in selectivity is negligible. Conversely, if the silver nitrate to phenol weight ratio is increased, the water concentration may also be increased, so that at a ratio of 2, the water concentration may advantageously be from about 19 to about 22% by weight.

In the preceding description of preferred compositions for the extracting solution of the present invention, silver nitrate is described as a preferred water soluble silver salt for use therein. As illustrative of other water soluble silver salts which may be employed may be mentioned the fluosilicate, perchlorate, fluoride, lactate, and acetate salts.

Any suitable type of apparatus may be employed in carrying out the process of the present invention for effecting the desired separation, which may be adapted to batch. intermittent, or

' weight of water.

continuous operation. After contacting the fluid hydrocarbon mixture with the absorbing solution. the resulting rafllnate and extract phases are separated, and the unsaturated hydrocarbon recovered from the extract phase. The unsaturated hydrocarbon recovery and regeneration of the extracting solution may be conveniently accomplished in one operation, such as by heating or reducing the pressure, orboth, in order to distill oil and/or desorb the absorbed unsaturated hydrocarbon, or by extraction of the unsaturated hydrocarbon with a second solvent which is substantially immiscible with the extracting solvent, and which may be subsequently separated from the unsaturated hydrocarbon, as for example by distillation. A suitable second solvent for such an operation, for example, is n-octane, which may be employed for extraction of unsaturated hydrocarbons in most instances.

The optimum temperature to be employed in the extraction step varies with the particular compound to be treated, and may range up to about 150 F. or more, but in most instances temperatures below F., and particularly those in the range of from about 32 to about 80 F. are suitable. At the relatively lower temperatures less phenol will be lost to the raillnate phase, but in any event such loss is usually slight. In general, atmospheric pressures are contemplated for use in the unsaturated hydrocarbon absorption step of the process of the present invention, especially where the fluid hydrocarbon being treated is a liquid under the conditions of the process, but subor super-atmospheric pressures may be employed where desirable.

As illustrative of a preferred embodiment of the present invention, a mixture of olefins and paraffins obtained from the thermal or catalytic cracking of a petroleum 011, wherein preferably the olefin contains from about 2 to 8 carbon atoms, or mixtures thereof, is contacted with an aqueous silver nitrate solution solutized with phenol, containing silver nitrate and phenol in quantities such that the weight ratio of silver nitrate to phenol is from about 0.4 to about 3, and preferably from about 1 to about 2, and containing from about 3% to about 40% by weight of water, and preferably from about 10% to about 22% by In carrying out the process of the present invention, the volume of hydrocarbon per volume of extracting solution employed may be varied considerably, the optimum value depending largely on the composition of the hydrocarbon mixture and the various operating conditions, but in most instances the volume ratio of hydrocarbon to extracting solution may advantageously be from about 0.1 to about 1. The temperature of the extraction step is preferably within the range of from about 32 to about 80 F., but the increase of absorption with decrease in temperature is not marked, and hence the economics of the process will usually dictate the use of ambient or atmospheric temperature. After contacting the hydrocarbon'and extracting solution, whether the process be of batch, intermittent or continuous type, the ramnate and extract phases are separated, the olefins recovered from the extract phase, preferably by distillation or solvent extraction, and the regenerated extracting solution recycled in the process.

The present invention may be better understood from a consideration oi the accompanying flow diagram which represents an embodiment of the present invention wherein a fluid hydrocarbon mixture containing the unsaturated hydrocarbon(s) to be separated is introduced into with the rafiinate leaving the extractor via line 5.

The first extract, which comprises the extracting solution (solvent) containing the extracted unsaturated hydrocarbon(s), passes out of the'extractor via line 6 and, where the unsaturated hydrocarbon(s) is stripped by a second solvent therefor, the first extract is passed into regenerator 8 via line 9. The second solvent, which is substantially immiscible with the extracting solution, is introduced into regenerator 8 via line Ill. The extracting solution oi. the first extract, flowing countercurrently to the second solvent, is stripped of the unsaturated hydrocarbon(s) then passes out of the .regenerator via line II. andis recycled to the extractor via lines ll, l2 and l. The second or stripping solvent containing the unsaturated hydrocarbon(s) passes from the re-' generator via lines I l and I5, through heat ex-- changer l6, and into a suitable stripper I8 fitted with heating means l9, such as a steam coil or the like. The unsaturated hydrocarbon(s) is stripped from the second solvent and passes from the stripper via line 20, and may be stored or may be otherwise treated, e. g., reacted to form derivatives thereof. The regenerated second solvent is recycled from the stripper into the regenerator via line 2!, heat exchanger l6, cooler 22 if desired (which may be operated by any convenient means, such as by cooling with water) and line Hi. When necessary or desirable, additional second solvent maybe introduced into the system via lines 1 and Hi.

When a second solvent is not employed, and the unsaturated hydrocarbon(s) is stripped from the extracting solutionby heat, the regenerator 8 is by-passed, the extracting solution passing from the extractor I via lines 6 and I5, through heat exchanger l6, and into stripper I8, where the unsaturated hydrocarbon(s) is stripped by heat, and leaves the stripper via line 20; The regenerated extracting solution is recycled irom'the stripper to the extractorvia line 2|, heat exchanger l6, cooler 22, and lines l3, l2 and 4. When it is necessary or desired to adjust or change the,composition of the extraction solution, silver salt, water and phenol may jointly or individually be introduced into the extractin solution via lines 22', 23, 24, 25, 26 and 21. I,

Various modifications in the above described apparatus and process may of course be employed, such as recycling the rafflnate through at least a portion of the extractor in order to obtain an especially pure rafllnate. For purposes of simplicity, pumps, temperature controls, control means, additional heat exchangers, andthe like, the proper placement of which is evident to those skilled in the art; have been largely omitted.

The main object of the present invention, the separation of unsaturated from less unsaturated hydrocarbons, has been described. It has also been found that the present invention may be employed to separate various classes of olefins. Thus, cyclic olefins are selectively absorbed from non-cyclic olefins, and olefins having the double bond in the alpha position are selectively absorbed from those wherein the double bond is in a difierent position, such as the beta position; while methyl and higher alkyl substituents on carbon atoms attached to the oleiinic bond somewhat reduces selectivity. For example, cyclopentene is absorbed selectively over straight chain 5 carbon atom olefins, 5 carbon atom olefins having the double bond in the alpha position are absorbed selectively over those with the. double bond in the beta position, while a methyl substituent on a carbon atom involved in the olefinic bond somewhat decreases selectivity.

By carrying out the process 0! the present invention, as herein described, surprisingly large amounts of olefin are absorbed per unit of solvent, which olefin may be easily recovered in substantially pure form. The extracting solution, after removal of the olefin, is recycled in the process, and is quite stable, when the herein described operating conditions are observed, only small losses of silver and phenol occurring, which, of course, may be recovered if desired.

Various modifications of the present invention, as herein described, may be employed, such as recycling the extracted hydrocarbon in .order to obtain an especially purified product, as above mentioned. This modification is especially desirable'where a more unsaturated hydrocarbon is separated from a less unsaturated hydrocarbon, since, although the more unsaturated hydrocarbon is preferentially extracted, some of the less unsaturated hydrocarbon will be also extracted, and recycling a portion of the extracted material is desirable in order to obtain substantial purity of the product. These and other modiflcations are within the scope of the present invention. Y

A further important embodiment of the present invention is to provide for the storage and transportation of unsaturated hydrocarbons. Since the lower unsaturated'hydrocarbons are gases at ordinary temperatures, and expand with increasing temperatures, it has been customary to employ strong and necessarily heavy containers for their storage and transportation. Due to the great solubility of unsaturated hydrocarbons in solutions ofwater-soluble silver salts in water and phenol, as herein described, such unsaturated hydrocarbons may conveniently be stored and transported while dissolved insaid solutions. For example, a solution of silver nitrate in phenol and water may be placed in a. suitable container, and a lower olefin, i. e., an olefin that is gaseous at ordinary temperatures and pressures, is introduced therein. It is usually advantageous to store the gas at a somewhat elevated pressure, since more will be dissolved thereby. The compositions of the absorbing so- ,lutions may be the same as those used for the separation of unsaturated hydrocarbons as herein described. Presures up to about 10 atmospheres generally are suitable, though high pressures maybe employed if desired. When it is desired to recover the gas, it may be easily removed from the solution by heating and/or reducingfie pressure, or by extracting with a solvent therefor which is immiscible in the solution. Solutions of unsaturated hydrocarbons in the solvents of the present invention, therefore, constitute new and useful compositions of matter.

The following examples illustrate the present invention, which is not to beconsidered as limited thereby:

EXAMPLEI fiotamixtureoffiand'lcanbonatomhydrocarbons containing 36.7% by volume oleflns, 57.5% by volume paraffins, and 5.8% by volume of aromatic compounds, were contacted with silver nitrate-phenol-water solutions of varying composition. All extractions were at atmospheric pressure and at the indicated temperatures. The compositions of the extracting solutions and results obtained are shown in Table I.

8 EXAMPLEIII Table I 2.2125225, 8:25.17 ggg gggjggg btsiisirszislsistaisii.

to Extractin AgNO; Phenol 11,0 32 F. 40 F. F. 80 F.

55.0 43.4 c. 0.14 1.7 1.4 so 57 4 C4 0. 57 7 15. 0 14. 3 42 50 s 05 0.44 11.8 11.5 41 42 17 c. 0.38 11 10.7 '10.1 5:4 25 22 O1 0. 37 as 8.4 7.6 7.0 01 19 05 0.4a 8.4 8.0 7.3 27 45 o. 0.27 5 s 5.5 5.9 25 C1 0.32 4.0 3.4 30.0 43.4 C4 7 0.14 0.7 0.5 .4 42 50 8 Cu 0.50 9.5 9.0

These data demonstrate the value of phenol volume percent increase on saturation with butaas a solutizer for aqueous silver nitrate solutions, diene was 26.1, or about 100% more than with that the compositions of the extracting solutions unsolutized aqueous silver nitrate. containing phenol may vary rather widely and I claim as my invention: good results achieved therewith, that the tem- 0 1. A process for the separation of olefins from perature of extraction may vary over a wide parafllns which comprises contacting a fluid hyrange without significantly adversely affecting drocarbon mixture containing olefinic and parafresults, and that high olefin extraction is favored finic hydrocarbons with a solution of silver nitrate by low water concentrations. in water and phenol wherein the silver nitrate In other similar experiments, but with the sub- 35 and phenol are present in weight ratio of silver stitution of other materials, including methanol, nitrate to phenol of from about 1 to about 2, and isopropanol, diacetone alcohol, ethanolamine nicontaining from about 10% to about 22% by trate, acetonitrile, ethylene glycol, and glycerine weight of water, respectively. for the phenol, with other experimental condi- 2. A process for the separation of olefins from tions comparable, the extracting powers of the 40 parafiins which comprises contacting a mixture solutions were greatly inferior to those obtained containing olefinic and parailinic hydrocarbons with phenol. with a solution of silver nitrate in water and EXAMPLE II phenol, wherein the silver nitrate and phenol are A catal mean cracked gasoline consisting present in weight ratio of silver nitrate to phenol chiefly of yfivewgrbon hydrocarbons containing 45 of from about 0.4 to about 3 and containing from about 42 percent by volume of five-carbon olefins about 3% to about 7 P welghtflof water was contacted with silver nitratemhenobwater selected so that the solution is substantially satusolutions of the compositions indicated in Table rated with to the Salt II. The extractions were performed at atmos- A process fol t P i of olefiqs from pheric pressure and F" with gasoline to hydrocarbon fraction within the gasoline boiltractive solvent volume ratios of from 0.15 to range and mntamulg 00th oleflmc and para! 0.40. The results are shown in Table II: i hydrocarbons which winpnses contacting said hydrocarbon fraction w1th a homogeneous Table II aqueous-phenolic solution of silver nitrate wherein the silver nitrate and phenol are present in Solvent Composition weight, ratio of silver nitrate to phenol of from N $3 5 $2 purity of about 2:3 to about 1:1 and the water is present Water Silvcrnitratc ,Per $5132 In the proportlons of m about 4% to about Per to phenpl w cent 12% by weight of the solution, respectively.-

y wt ram 4. A process for the separation or oleflns from parafilns which comprise contacting a fluid mixig- 1:3 8%, ture containing olefinic and parafllnic hydrocar- 21.0 1.0 7.15 95.5 bons with a homogeneous-aqueous phenol solufg g i gig tion of a water-soluble silver salt selected from 15 0. 42 5.07 70.0 the group consisting of silver nitrate, silver fluo- 8 g: g"; silicate, silver fluoride, silver perchlorate, silver 22 2.12 7.5 9518 lactate and silver acetate, wherein the silver salt and phenol are present in weight ratio of silver salt to phenol of from about 0.4 to about 3 and These data show the value of employing a 501- 7 the solution contains from about 3% to about vent with relatively small amounts of water, a small but noticeable decrease in the selectivity of absorption at low silver nitrate to phenol ratios, and generally high olefin absorption and selectivity.

40% by weight of water selected so that the solution is substantially saturated with respect to the silver salt. 1

5. A process for the separation of butadiene from a hydrocarbon mixture of butadiene and 9 less unsaturated hydrocarbons which comprises contacting said mixture with a homogeneous aqueous-phenol solution of silver nitrate, said solution containing silver nitrate, phenol and water in the proportions by weight, respectively, of about 40:40:20.

6. A process for the separation 01 unsaturated hydrocarbons from a hydrocarbon mixture containing the same which comprises; contacting said hydrocarbon mixture with a homogeneous aqueous-phenol solution of a water-soluble silver salt selected from the group consisting of silver nitrate, sflver fluosilicate, silver fluoride, silver perchlorate, silver lactate and silver acetate wherein the silver salt and phenol are present in the weight ratio of silver salt to phenol of about 1 and said solution contains about 10 to 12% by weight water.

7. A process for the separation of unsaturated hydrocarbons from a hydrocarbon mixture containing the same which comprises; contacting said hydrocarbon with a homogeneous aqueousphenol solution of a water-soluble silver salt selected from the group consisting of silver nitrate, silver fluosilicate, silver fluoride, silver perchlorate, silver lactate and silver acetate wherein the silver salt and phenol are present in the weight ratio of silver salt to phenol between about 0.4 and'about 3 and said solution is substantially saturated with respect to the silver salt.

8. A process for the separation of unsaturated hydrocarbons from a hydrocarbon mixture containing the same which comprises; contacting said hydrocarbon with a homogeneous aqueousphenol solution of a water-soluble sflver salt selected from the group consisting of silver mtrate, silver fluosilicate, silver fluoride, silver perchlorate, silver lactate and silver acetate wherein the sflver salt and phenol are present in the weight ratio of silver salt to phenol between about 0.4 and about 1 and said solution is substantially saturated with respect to the silver salt.

9. A process for the Separation of unsaturated hydrocarbons from a fluid hydrocarbon mixture containing the same and less unsaturated hydrocarbons which comprises; contacting said hydrocarbon mixture with a homogeneous aqueousphenol solution of silver nitrate wherein the weight ratio of silver nitrate to phenol is about 1 and said solution contains about 10 to 12% by weight water.

10. A process for the separation of unsaturated hydrocarbons from a fluid hydrocarbon mixture containing the same and less unsaturated hydrocarbons which comprises; contacting said hydrocarbon mixture with a homogeneous aqueousphenol solution of silver nitrate wherein the weight ratio of silver nitrate to phenol is between about 0.4 and about 3 and said solution is substantially saturated with respect to silver nitrate.

11. A prom for the separation of unsaturated hydrocarbons from a fluid hydrocarbon mixture containing the same and less unsaturated hydrocarbons which comprises; contacting said hydrocarbon mixture with a homogeneous aqueousphenol solution of silver nitrate wherein the weight ratio of silver nitrate to phenol is between about 0.4 and about 1 and said solution is substantially saturated with respect to silver nitrate.

ROBERT M. COLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED SIATES PA'I'ENTS Number Name Date 2,139,000 Cohen Dec. 6, 1938 2,235,119 Robey Mar. 18, 1941 2,246,257 Kohn June 17, 1941 2,391,404 Friedman et a1 Dec. 25, 1945 2,395,957 Breuer Mar. 5, 1946 2,407,820 Durrum Sept. 17, 1946 2,463,482 Francis Mar. 1, 1949 

1. A PROCESS FOR THE SEPARATION OF OLEFINS FROM PARAFFINS WHICH COMPRISES CONTACTING A FLUID HYDROCARBON MIXTURE CONTAINING OLEFINIC AND PARAFFINIC HYDROCARBONS WITH A SOLUTION OF SILVER NITRATE IN WATER AND PHENOL WHEREIN THE SILVER NITRATE AND PHENOL ARE PRESENT IN WEIGHT RATIO OF SILVER NITRATE TO PHENOL OF FROM ABOUT 1 TO ABOUT 2, AND CONTAINING FROM ABOUT 10% TO ABOUT 22% BY WEIGHT OF WATER, RESPECTIVELY. 